The present invention relates to the medical imaging arts. It particularly relates to angiography using the magnetic resonance imaging (MRI) and computed tomography (CT) medical imaging techniques, and will be described with particular reference thereto. However, the invention will also find application in conjunction with other three-dimensional imaging modalities as well as in other imaging arts in which thin structures or networks with overlapping or furcated portions are advantageously differentiated from extraneous imaged structures and background noise or tracked in three dimensions.
Catastrophic medical events such as heart attacks and strokes that result from underlying vascular problems are a leading cause of death in the United States. Plaque buildup on the inside of the vascular walls can lead to strokes, coronary heart disease, and other medical conditions such as vessel rupture. Many Americans suffer from chronic vascular diseases which degrade quality of life.
Angiography relates to the imaging of blood vessels and blood vessel systems, and as such is a powerful medical diagnostic for identifying and tracking vascular diseases. Angiography enables improved surgical planning and treatment, improved diagnosis and convenient non-invasive monitoring of chronic vascular diseases, and can provide an early indication of potentially fatal conditions such as aneurysms and blood clots. The ability of certain types of angiography to accurately characterize the vessel lumen is particularly valuable for diagnosing plaque buildup on the vessel walls.
Angiography is performed using a number of different medical imaging modalities, including biplane X-ray/DSA, magnetic resonance (MR), computed tomography (CT), ultrasound, and various combinations of these techniques. Two-dimensional or three-dimensional angiographic data can be acquired depending upon the medical imaging modality and the selected operating parameters. Certain types of angiography employ invasive contrast enhanced methodologies in which a contrast agent that accentuates the vascular image contrast is administered to the patient prior to the imaging session. Some angiography techniques, such as MR imaging, are also capable of providing vascular contrast using non-invasive methodologies that take advantage of intrinsic aspects of the vascular system, such as the blood motion or flow, to enhance the vascular contrast without employing an administered contrast agent. For either contrast-enhanced or non-contrast-enhanced angiography, the vasculature imaging is effectuated by either a signal enhancement in the vascular regions (white blood angiography), or by a signal suppression in the vascular regions (black blood angiography).
The analysis of angiographic images by medical personnel is often hindered by image imperfections or intervening non-vascular structures (e.g., bone, organs, and the like). Even in the absence of such problems, however, the sheer complexity of the vascular system and its myriad sub-systems severely complicates image interpretation.
With reference to FIG. 1, a schematic portion of an exemplary vasculature is shown, including an arterial sub-system A and a venous sub-system V. As is often the actual situation in the human body, the two sub-systems A, V are shown in FIG. 1 arranged in a substantially parallel manner. Furthermore, there are numerous points where, in the view shown, an artery portion overlaps a vein portion: exemplary points are designated AV. Similarly, there are numerous points where the a vein portion overlaps an artery portion: exemplary points are designated VA. Another complexity arises at furcation points. FIG. 1 shows exemplary artery bifurcations AB and exemplary vein bifurcations VB.
With reference to FIG. 2, an exemplary vascular crossing is shown, in which a vessel V1 and a vessel V2 cross. In three-dimensional angiography, the image is typically created by imaging a plurality of parallel planes S which are then combined to form a three-dimensional image representation. For an exemplary slice So oriented perpendicular to the vessels V1 and V2, the image of the vessel V1 in the plane So is shown superimposed as W1. Similarly the image of the vessel V2 in the plane So is shown superimposed as W2.
With reference to FIG. 3A, it is seen that the vessel images W1 and W2 are overlapping in the image slice So. FIG. 3B shows the overlapping vessel images W1 and W2 as they would appear in a typical angiographic image. Since the contrast is essentially identical for W1 and W2, it will not be clear to medical personnel whether the overlapping vessels represent crossing arteries, crossing veins, an artery crossing a vein, a vein crossing an artery, a vein bifurcation point, an artery bifurcation point, a closely positioned but non-overlapping pair of vessels, et cetera.
The vascular complexity issues described with reference to FIGS. 1 through 3B are advantageously addressed by automated vascular segmentation systems. These systems differentiate the vasculature from non-vascular structures, background levels, imaging system artifacts such as noise, and the like. Many segmentation engines employ tracking systems which track a vessel starting from an initial seed location. Tracking systems can track the vessel skeleton while simultaneously quantifying the vessel lumen, and such systems are particularly useful for accommodating the varying vessel diameters usually encountered in following a blood vessel. Tracking systems also can separate out individual vessel branches. In the exemplary FIG. 1, a tracking system starting at artery seed AS will track the arterial branch A, while the tracking system starting at vein seed VS will track the venous branch V. In this manner, artery-vein separation is achievable.
However, tracking methods of the prior art have numerous disadvantages, principally due to the localized nature of the tracking analysis. Tracking can be cumbersome and inaccurate, particularly in areas of very high vascular densities such as in the brain. Bifurcation points, tortuous or occluded vessels, vessel overlaps, intertwined vessels, partial volume averaging and other imaging artifacts, and vessel gaps can act alone or in various combinations to produce localized disjoints of the vascular path (or localized disjoints of the angiographic image of the vascular path) which prevent successful vessel tracking. Furthermore, at vessel overlaps the wrong vascular system may be tracked. For example, a tracking system following the arterial branch A of FIG. 1 could fail and begin tracking the venous branch V at any of the crossing points AV, VA.
The present invention contemplates an improved angiographic method and apparatus which overcomes the aforementioned limitations and others.